[WIP] Add support for class member variable

I've submitted this PR as WIP to get feedback, **the code does not work for now**

I am looking for:
- feedback on the implemenation,
- how to debug (currently I'm doing make + node debug which is not the most user friendly workflow),
- what kind of test should be added.

/cc @arv
This is not the right one. You need to use the internalName here. Also, a general tip is to keep this a token so that source maps can map thing back and forth.